Secondary battery and electronic device

ABSTRACT

To provide a secondary battery that is suitable to a portable information terminal or a wearable device. To provide an electronic device having a novel structure that can have various forms and a secondary battery that fits the forms of the electronic device. The secondary battery includes a film provided with depressions or projections that can ease stress on the film due to application of external force. The sizes of the depressions or projections are different between a center portion and an end portion of the film. The end portion of the film is sealed with an adhesive layer. The depressions or projections of the film are formed by pressing such as embossing.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an object, a method, or a manufacturingmethod. The present invention relates to a process, a machine,manufacture, or a composition of matter. One embodiment of the presentinvention relates to a semiconductor device, a display device, alight-emitting device, a power storage device, a driving method thereof,or a manufacturing method thereof. In particular, one embodiment of thepresent invention relates to an electronic device.

Note that electronic devices in this specification mean all devicesincluding secondary batteries, and electro-optical devices includingsecondary batteries, information terminal devices including secondarybatteries, vehicles including secondary batteries, and the like are allelectronic devices.

2. Description of the Related Art

In recent years, portable information terminals typified by smartphoneshave been actively developed. Portable information terminals, which area kind of electronic devices, are desired to be lightweight and compactby users.

Patent Document 1 discloses an example of a hands-free wearable devicewith which information can be visually obtained anywhere, specifically,a goggle-type display device that includes a CPU and is capable of datacommunication. The device disclosed in Patent Document 1 is also a kindof electronic device.

Most wearable devices and portable information terminals includesecondary batteries that can be repeatedly charged and discharged, andhave problems in that there is a limitation on the time for operation ofthe wearable devices and the portable information terminals becausetheir light weight and compactness limit the battery capacity. Secondarybatteries used in wearable devices and portable information terminalsshould be lightweight and compact and should be able to be used for along time.

Examples of secondary batteries include a nickel-metal hydride batteryand a lithium-ion secondary battery. In particular, lithium-ionsecondary batteries have been actively researched and developed becausethe capacity thereof can be increased and the size thereof can bereduced.

Electrodes serving as positive electrodes or negative electrodes oflithium-ion secondary batteries are each formed using, for example,lithium metal, a carbon-based material, or an alloy material.

REFERENCE

[Patent Document 1] Japanese Published Patent Application No.2005-157317

SUMMARY OF THE INVENTION

An object is to provide a secondary battery suitable for a portableinformation terminal.

Another object is to provide a secondary battery suitable for a wearabledevice. Another object is to provide a novel power storage device.

Another object is to provide an electronic device having a novelstructure, specifically, an electronic device having a novel structurethat can be changed in appearance in various ways. Another object is toprovide an electronic device having a novel structure that can havevarious forms and a secondary battery that fits the forms of theelectronic device.

Note that the descriptions of these objects do not disturb the existenceof other objects. In one embodiment of the present invention, there isno need to achieve all the objects. Other objects will be apparent fromand can be derived from the descriptions of the specification, thedrawings, the claims, and the like.

In the case where an electronic device is formed to have a complicatedform, a housing is designed to have a complicated form and electroniccomponents (e.g., a power source, a wiring, a transistor, a resistor,and a capacitor) are arranged in an internal space of the housing. Whenit does not matter how large and heavy the electronic device is, thevolume of the internal space of the housing is relatively large; thus,the electronic components can be arranged relatively freely.

In the case where an electronic device having a complicated form isrequired to be compact and lightweight, the volume of an internal spaceof a housing is small, and electronic components and the sizes thereofare selected according to the volume and the electronic components arearranged. In this case, the manufacturing cost is increased becausesmaller electronic components are more expensive.

Moreover, as the volume or weight of a secondary battery increases, thecapacity thereof tends to increase. Therefore, there are limitations onthe size and arrangement of a secondary battery that is incorporated ina small electronic device.

An increase in the mileage per charge of a vehicle using a secondarybattery such as an electric vehicle and a hybrid vehicle increases thevolume or weight of the secondary battery.

In view of the above, a secondary battery that can be changed in form isused for an electronic device and the secondary battery and otherelectronic components are arranged with efficiency in the internal spaceof a housing of the electronic device.

In the case where a secondary battery is changed in form by externallyapplying force, the force is externally applied to an object such as afilm used as an exterior body of the secondary battery and the object isstressed. This might partly deform or damage the object.

A secondary battery that can relieve a strain caused by stress isprovided. A “strain” is the scale of change in form indicating thedisplacement of a point of an object relative to the reference (initial)length of the object. A secondary battery that can reduce the influenceof a strain, that is, the scale of change in form caused by applicationof external force to the secondary battery, to an acceptable level isprovided. Such a structure as can relieve a strain caused by stress canprevent the secondary battery (e.g., an exterior body) from beingdamaged when changed in form by being bent, for example, achievinglong-time reliability.

One embodiment of the invention disclosed in this specification is asecondary battery including a film provided with depressions orprojections that can ease stress on the film due to application ofexternal force. The heights of the depressions or projections aredifferent between a center portion and an end portion of the film. Theend portion of the film is sealed with an adhesive layer.

Another embodiment of the invention disclosed in this specification is asecondary battery including a film having a pattern formed bydepressions or projections on part of a surface thereof. The heights ofthe depressions or projections are different between a center portionand an end portion of the film. The end portion of the film is sealedwith an adhesive layer.

In the above structure, the pattern of the film is a geometric patternin which lines slanted in two directions cross each other and which canbe visually recognized. In the case of such a geometric pattern in whichlines slanted in two directions cross each other, stress due to bendingcan be relieved in at least two directions. The depressions orprojections are not necessarily arranged regularly and may be arrangedrandomly. Random arrangement enables stress due to not onlytwo-dimensional bending but stress due to three-dimensional randombending or twisting to be relieved. The film may partly include aplurality of regions having different patterns. The film may be providedwith depressions or projections only in a bendable portion and may havea flat surface in the other portion.

The depressions or projections of the film are formed by pressing, e.g.,embossing. The depressions or projections of a surface (or a rearsurface) of the film formed by embossing form an obstructed space thatis sealed by the film serving as a part of a wall of the sealingstructure and whose inner volume is variable. It can be said that thedepressions or projections of the film form an accordion structure(bellows structure) in this obstructed space. The sealing structureusing the film can prevent entry of water and dust. Note that embossing,which is a kind of pressing, is not necessarily employed and any methodthat allows formation of a relief on part of the film is employed. Acombination of the methods, for example, embossing and any otherpressing may be performed on one film. Alternatively, embossing may beperformed on one film more than once.

Although the secondary battery can have any of a variety of structures,a structure where a film is used as an exterior body is employed here.Note that the film used as an exterior body is a single-layer filmselected from metal films (e.g., an aluminum film, a stainless steelfilm, and a nickel steel film), a plastic film made of an organicmaterial, a hybrid material film containing an organic material (e.g.,an organic resin or fiber) and an inorganic material (e.g., ceramic),carbon-containing films (e.g., a carbon film and a graphite film), andthe like or a layered film including two or more of the above films.Metal films are easy to be embossed. Forming depressions or projectionsby embossing increases the surface area of the film exposed to outsideair, achieving efficient heat dissipation.

The sealing structure of the secondary battery is as follows: onerectangular film is folded in half so that two end portions eachincluding two of the four corners overlap with each other (the foldedportion is sandwiched between the end portions) and is sealed on threesides with an adhesive layer, or two films are stacked so as to overlapwith each other and is sealed on four sides of the film with an adhesivelayer.

The adhesive layer can be formed using a thermoplastic film material, athermosetting adhesive, an anaerobic adhesive, a photo-curable adhesivesuch as a UV curable adhesive, or a reactive curable adhesive. Examplesof materials of the adhesives include an epoxy resin, an acrylic resin,a silicone resin, and a phenol resin.

In forming the sealing structure by bonding and fixing the adhesivelayer and the film, pressure bonding is performed so that the heights ofthe depressions or projections are different between an end portion ofthe film, which is subjected to pressure bonding, and a center portionof the film. When the height of the depressions or projections in theend portion of the film is smaller than that of the depressions orprojections in the center portion of the film, the influence of a straincan be reduced to be within the allowable range.

In the case where a film is provided with depressions or projections ina center portion and not provided with depressions or projections in anend portion subjected to pressure bonding, the obstructed space of thesecondary battery can greatly expand when the volume of internalcomponents of the secondary battery expands in the center portion. Thatis, such a film can prevent explosion of the secondary battery. On theother hand, because of absence of depressions or projections in the endportion, flexibility of the end portion is lower than that in the centerportion and stress is less likely to be relieved in the end portion thanin the center portion. Therefore, providing depressions or projectionsalso in the end portion of the film helps reduce the influence of astrain to an acceptable level.

The term “electronic device having a complicated form” can beinterpreted in many ways. It can be interpreted as an electronic devicehaving a fixed complicated form (e.g., the form having a curvedsurface). In the case of fixing the form of the electronic device, asecondary battery is bent once and fixed while being bent. In addition,the term can also be interpreted as an electronic device having acomplicated form that changes or does not change its form when externalforce is applied or an electronic device having a simple form thatchanges its form when external force is applied. In the case of anelectronic device that changes its form when force is applied, it ispreferable that a secondary battery also be able to change its formevery time force is applied.

One embodiment of the invention disclosed in this specification is anelectronic device including a housing partly having a curved surface anda secondary battery having a curved surface. An exterior body of thesecondary battery is a film whose surface partly has a pattern formed bydepressions or projections.

Another embodiment of the invention disclosed in this specification isan electronic device including a housing and a secondary battery incontact with part of the housing. An exterior body of the secondarybattery is a film whose surface partly has a pattern formed bydepressions or projections. The housing can partly change its form.

In the above structure, the exterior body of the secondary battery canchange its form in the range of radius of curvature from 10 mm to 150mm, preferably from 30 mm to 150 mm. One or two films are used as theexterior body of the secondary battery. In the case where the secondarybattery has a layered structure and the secondary battery has anarc-formed cross section by bending the secondary battery, the secondarybattery has a structure where the components thereof is sandwichedbetween two curved surfaces of the films.

A description is given of the radius of curvature of a surface withreference to FIGS. 19A to 19C. In FIG. 19A, on a plane 1701 along whicha curved surface 1700 is cut, part of a curve 1702, which is a form ofthe curved surface, is approximate to an are of a circle, and the radiusof the circle is referred to as a radius 1703 of curvature and thecenter of the circle is referred to as a center 1704 of curvature. FIG.19B is a top view of the curved surface 1700. FIG. 19C is across-sectional view of the curved surface 1700 taken along the plane1701. When a curved surface is cut along a plane, the radius ofcurvature of a curve depends on along which plane the curved surface iscut. Here, the radius of curvature of a curved surface is defined as theradius of curvature of a curve on a plane along which the curved surfaceis cut such that the curve has the smallest radius of curvature.

In the case of bending a secondary battery in which a component 1805including electrodes and an electrolytic solution is sandwiched betweentwo films as exterior bodies, a radius 1802 of curvature of a film 1801close to a center 1800 of curvature of the secondary battery is smallerthan a radius 1804 of curvature of a film 1803 far from the center 1800of curvature (FIG. 20A). When the secondary battery is curved and has anarc-shaped cross section, compressive stress is applied to a surface ofthe film on the side closer to the center 1800 of curvature and tensilestress is applied to a surface of the film on the side farther from thecenter 1800 of curvature (FIG. 20B). However, by forming a patternincluding projections or depressions on surfaces of the exterior bodies,the influence of a strain can be reduced to be acceptable even whencompressive stress and tensile stress are applied. For this reason, thesecondary battery can change its form such that the exterior body on theside closer to the center of curvature has a curvature radius greaterthan or equal to 10 mm, preferably greater than or equal to 30 mm

Note that the cross-sectional shape of the secondary battery is notlimited to a simple are shape, and the cross section can be partlyarc-shaped; for example, a shape illustrated in FIG. 20C, a wavy shapeillustrated in FIG. 20D, or an S shape can be used. When the curvedsurface of the secondary battery has a shape with a plurality of centersof curvature, the secondary battery can change its form such that acurved surface with the smallest radius of curvature among radii ofcurvature with respect to the plurality of centers of curvature, whichis a surface of the exterior body on the side closer to the center ofcurvature, has a curvature radius greater than or equal to 10 mm,preferably greater than or equal to 30 mm.

When the secondary battery is bent with the center of curvature being onthe inner side and seen in cross section, the outside surface isstretched and the inside surface is compressed. In other words, theoutside expands and the inside contracts. The bendable secondary batterycan also be called an elastic secondary battery.

When a secondary battery in which an electrolyte solution is heldbetween two films serving as exterior bodies is bent, the radius ofcurvature of a first film is smaller than that of a second film. Inaddition, in the secondary battery, a pattern of a surface of the firstfilm is different from that of the second film. When the secondarybattery is bent and has an arc-shaped cross section, compressive stressis applied to a surface of the film on the side closer to the center ofcurvature and tensile stress is applied to a surface of the film on theside farther from the center of curvature. Even when compressive stressor tensile stress is applied to a film surface in such a manner, theinfluence of a stain is allowable because a surface of the exterior bodyhas a pattern formed by depressions or projections.

Part of a device like a watch is brought in contact with part of thebody of a user, that is, the user wears the device, whereby the user canfeel like the device is lighter than the actual weight. The use of aflexible secondary battery in an electronic device having a form with acurved surface that fits part of the body of a user allows the secondarybattery to be fixed so as to have a form suitable to the electronicdevice and provided.

When a user moves part of the body on which an electronic device isworn, the user might feel uncomfortable, regard the electronic device asa distraction, and feel stress even in the case where the electronicdevice has a curved surface that fits part of the body. In the casewhere at least part of an electronic device can be changed in formaccording to movement of a body of a user, the user does not feeluncomfortable and a flexible battery can be provided in a portion of theelectronic device that can be changed in form.

An electronic device does not necessarily have a form with a curvedsurface or a complicated form; an electronic device may have a simpleform. For example, the number or size of components that can beincorporated in an electronic device with a simple form is determineddepending on the volume of a space formed by a housing of the electronicdevice in many cases. Providing a flexible secondary battery in a smallspace between components other than the secondary battery enables aspace formed by a housing of an electronic device to be efficientlyused; thus, the electronic device can be reduced in size.

Examples of wearable devices include wearable input terminals such as awearable camera, a wearable microphone, and a wearable sensor, wearableoutput terminals such as a wearable display and a wearable speaker, andwearable input/output terminals having the functions of any of the inputterminals and any of the output terminals. Another example of a wearabledevice is a device that controls each device and calculates or processesdata, typically, a wearable computer including a CPU. Other examples ofwearable devices include devices that store data, send data, and receivedata, typically, a portable information terminal and a memory.

A secondary battery having a novel structure can be provided. A novelpower storage device can be provided.

The form of a secondary battery can be freely designed and when asecondary battery having a curved surface is used for example, theflexibility of a whole device is increased and devices having a varietyof designs can be fabricated. Furthermore, a secondary battery isprovided inside and along a curved surface of a device with the leastwasted space in the device having the curved surface, whereby it ispossible to make maximum use of a space in the device.

Thus, an electronic device having a novel structure can be provided.

Note that the description of these effects does not disturb theexistence of other effects. One embodiment of the present invention doesnot have to achieve all the objects listed above. Other effects will beapparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B are top views each illustrating one embodiment of thepresent invention;

FIGS. 2A to 2F are perspective views illustrating one embodiment of thepresent invention;

FIGS. 3A to 3C each illustrate embossing of one embodiment of thepresent invention;

FIGS. 4A to 4E are top views illustrating one embodiment of the presentinvention;

FIGS. 5A and 5B are perspective views each illustrating one embodimentof the present invention;

FIGS. 6A and 6B are perspective views illustrating one embodiment of thepresent invention;

FIGS. 7A and 7B are top views each illustrating an embodiment of thepresent invention;

FIGS. 8A and 8B are perspective views each illustrating one embodimentof the present invention;

FIG. 9A is an external photograph of a secondary battery of oneembodiment of the present invention, and FIG. 9B is a schematic viewthereof;

FIG. 10A is an X-ray photograph of a secondary battery of one embodimentof the present invention, and FIG. 10B is a schematic view thereof;

FIG. 11A is a cross-sectional view of an electronic device of oneembodiment of the present invention, and FIG. 11B is an externalphotograph thereof;

FIGS. 12A and 12B are external photographs of an electronic device ofone embodiment of the present invention;

FIGS. 13A to 13H illustrate electronic devices including flexiblesecondary batteries;

FIGS. 14A and 14B illustrate vehicles including secondary batteries;

FIGS. 15A and 15B are external perspective views illustrating anelectronic device of one embodiment of the present invention;

FIGS. 16A to 16D each illustrate an electronic device;

FIGS. 17A to 17C are external photographs of an electronic device of oneembodiment of the present invention;

FIG. 18 is a schematic cross-sectional view of FIG. 12A;

FIGS. 19A to 19C illustrate a radius of curvature of a surface;

FIGS. 20A to 20D illustrate a center of curvature;

FIGS. 21A and 21B are photographs of a bend tester;

FIGS. 22A to 22E are X-ray CT photographs, FIG. 22F is an externalphotograph, and FIG. 22G is a graph showing charge and dischargecharacteristics;

FIGS. 23A to 23E are X-ray CT photographs, FIG. 23F is an externalphotograph, and FIG. 23G is a graph showing charge and dischargecharacteristics; and

FIGS. 24A and 24B are graphs showing charge characteristics anddischarge characteristics.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments and examples of the present invention will be describedbelow in detail with reference to the drawings. However, the presentinvention is not limited to the descriptions below, and it is easilyunderstood by those skilled in the art that modes and details disclosedherein can be modified in various ways. Further, the present inventionis not construed as being limited to the descriptions of the embodimentsand the examples.

The term “electrically connected” includes the case where components areconnected through an “object having any electric function”. There is noparticular limitation on the “object having any electric function” aslong as electric signals can be transmitted and received between thecomponents connected through the object.

The position, size, range, or the like of each component illustrated indrawings and the like is not accurately represented in some cases forsimplification. Therefore, the disclosed invention is not necessarilylimited to the position, size, range, or the like disclosed in thedrawings and the like.

The ordinal number such as “first”, “second”, and “third” are used toavoid confusion among components.

Note that in this specification, a term “parallel” indicates that theangle formed between two straight lines is greater than or equal to −10°and less than or equal to 10°, and accordingly also includes the casewhere the angle is greater than or equal to −5° and less than or equalto 5°. In addition, the term “perpendicular” indicates that the angleformed between two straight lines is greater than or equal to 80° andless than or equal to 100° and accordingly also includes the case wherethe angle is greater than or equal to 85° and less than or equal to 95°.

Embodiment 1

In this embodiment, an example of fabricating a lithium-ion secondarybattery with the use of a film whose surface is embossed with a patternwill be described.

First, a sheet made of a flexible material is prepared. As the sheet, astacked body, a metal film provided with an adhesive layer (alsoreferred to as a heat-seal layer) or sandwiched between adhesive layersis used. As the adhesive layer, a heat-seal resin film containing, e.g.,polypropylene or polyethylene is used. In this embodiment, a metalsheet, specifically, aluminum foil whose top surface is provided with anylon resin and whose bottom surface is provided with a stack includingan acid-proof polypropylene film and a polypropylene film is used as thesheet. This sheet is cut to obtain a film 10 illustrated in FIG. 1A.

Then, the film 10 is embossed to form unevenness so that the pattern canbe visually recognized as illustrated in FIG. 1B. Although an examplewhere the sheet is cut and then embossing is performed is describedhere, the order is not particularly limited; embossing may be performedbefore cutting the sheet and then the sheet is cut so as to be in thestate illustrated in FIG. 1B. Alternatively, the sheet may be cut afterthermocompression bonding is performed with the sheet bent.

Embossing, which is a kind of pressing, will be described.

FIGS. 3A to 3C are cross-sectional views each showing an example ofembossing. Note that embossing refers to processing for formingunevenness on a surface of a film by bringing an embossing roll whosesurface has unevenness into contact with the film with pressure. Theembossing roll is a roll whose surface is patterned.

An example where one surface of a film is embossed is illustrated inFIG. 3A.

FIG. 3A illustrates the state where a film 50 is sandwiched between anembossing roll 53 in contact with the one surface of the film and a roll54 in contact with the other surface and the film 50 is beingtransferred in a direction 58 of movement of the film 50. The surface ofthe film is patterned by pressure or heat.

Processing illustrated in FIG. 3A is called one-side embossing performedby a combination of the embossing roll 53 and the roll 54 (a metal rollor an elastic roll (e.g., rubber roll)).

An example where both surfaces of a film are embossed is illustrated inFIG. 3B.

FIG. 3B illustrates the state where a film 51 is sandwiched between theembossing roll 53 in contact with one surface of the film and anembossing roll 55 in contact with the other surface and the film 51 isbeing transferred in the direction 58 of movement of the film 51.

Processing illustrated in FIG. 3B is called both-side embossingperformed by a combination of the embossing roll 53 and the embossingroll 55, which are a couple of embossing rolls.

The surface of the film 51 is patterned by unevenness, that is,projections for concaving part of the surface of the film anddepressions for convexing part of the surface of the film that arealternately provided.

FIG. 3C illustrates the state where a film 52 is sandwiched between anembossing roll 56 in contact with one surface of the film and anembossing roll 57 in contact with the other surface and the film 52 isbeing transferred in the direction 58 of movement of the film 52.

Processing illustrated in FIG. 3C is called Tip to Tip both-sideembossing performed by a combination of the embossing roll 56 and theembossing roll 57 that has the same pattern as the embossing roll 56.The phases of the projections and depressions of the two embossing rollsare the same, so that substantially the same pattern can be formed onthe top surface and bottom surface of the film 52.

The embossing roll is not necessarily used, and an embossing plate maybe used. Furthermore, embossing is not necessarily employed, and anymethod that allows formation of a relief on part of the film isemployed.

In this embodiment, both surfaces of a film 11 are provided withunevenness to have patterns, and the film 11 is folded in half so thattwo end portions each including two of the four corners overlap witheach other, and is sealed on three sides with an adhesive layer.

Then, the film 11 is folded along a dotted line shown in FIG. 1B so asto be in the state illustrated in FIG. 2A.

A positive electrode current collector 12, a separator 13, and anegative electrode current collector 14 that are stacked and included ina secondary battery as illustrated in FIG. 2B are prepared. The positiveelectrode current collector 12 and the negative electrode currentcollector 14 can each be formed using a highly conductive material thatis not alloyed with a carrier ion of, for example, lithium, such as ametal typified by stainless steel, gold, platinum, zinc, iron, nickel,copper, aluminum, titanium, and tantalum or an alloy thereof.Alternatively, an aluminum alloy to which an element which improves heatresistance, such as silicon, titanium, neodymium, scandium, andmolybdenum, is added can be used. Still alternatively, a metal elementwhich forms silicide by reacting with silicon can be used. Examples ofthe metal element which forms silicide by reacting with silicon includezirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium,molybdenum, tungsten, cobalt, nickel, and the like. The currentcollectors can each have a foil-like shape, a plate-like shape(sheet-like shape), a net-like shape, a cylindrical shape, a coil shape,a punching-metal shape, an expanded-metal shape, or the like asappropriate. The current collectors each preferably have a thickness of10 μm to 30 μm inclusive. Note that the example where one combination ofthe positive electrode current collector 12, the separator 13, and thenegative electrode current collector 14 that are stacked is packed in anexterior body is illustrated here for simplicity. To increase thecapacity of a secondary battery, a plurality of combinations may bestacked and packed in an exterior body.

In addition, two lead electrodes 16 with sealing layers 15 illustratedin FIG. 2C are prepared. The lead electrodes 16 are each also referredto as a lead terminal and provided in order to lead a positive electrodeor a negative electrode of a secondary battery to the outside of anexterior film.

Then, one of the lead electrodes is electrically connected to aprotruding portion of the positive electrode current collector 12 byultrasonic welding or the like. Aluminum is used as a material of thelead electrode connected to the protruding portion of the positiveelectrode current collector 12. The other lead electrode is electricallyconnected to a protruding portion of the negative electrode currentcollector 14 by ultrasonic welding or the like. Nickel-plated copper isused as a material of the lead electrode connected to the protrudingportion of the negative electrode current collector 14.

Then, two sides of the film 11 are sealed by thermocompression bonding,and one side is left open for introduction of an electrolytic solution.In thermocompression bonding, the sealing layers 15 provided on the leadelectrodes are also melted, thereby fixing the lead electrodes and thefilm 11 to each other. After that, in a reduced-pressure atmosphere oran inert atmosphere, a desired amount of electrolytic solution isintroduced to the inside of the film 11 in the form of a bag. Lastly,the outer edge of the film that has not been subjected tothermocompression bonding and is left open is sealed bythermocompression bonding.

In this manner, a secondary battery 40 illustrated in FIG. 2D can befabricated.

In the obtained secondary battery 40, the surface of the film 11 servingas an exterior body has a pattern including unevenness. An edge regionindicated by a dotted line in FIG. 2D is a thermocompression-bondedregion 17. A surface of the thermocompression-bonded region 17 also hasa pattern including unevenness. Although the unevenness in thethermocompression-bonded region 17 is smaller than that in a centerportion, it can relieve stress applied when the secondary battery isbent. Such a structure as can relieve a strain caused by stress canprevent the secondary battery (e.g., an exterior body) from beingdamaged when changed in form by being bent, for example, achievinglong-time reliability.

FIG. 2E illustrates an example of a cross section taken alongdashed-dotted line A-B in FIG. 2D.

As illustrated in FIG. 2E, unevenness of the film 11 is differentbetween a region overlapping with the positive electrode currentcollector 12 and the thermocompression-bonded region 17. As illustratedin FIG. 2E, the positive electrode current collector 12, a positiveelectrode active material layer 18, the separator 13, a negativeelectrode active material layer 19, and the negative electrode currentcollector 14 are stacked in this order and placed inside the folded film11, an end portion is sealed with an adhesive layer 30, and the otherspace is provided with an electrolytic solution 20.

Examples of positive electrode active materials that can be used for thepositive electrode active material layer 18 include a composite oxidewith an olivine structure, a composite oxide with a layered rock-saltstructure, and a composite oxide with a spinel structure. Specifically,a compound such as LiFeO₂, LiCoO₂, LiNiO₂, LiMn₂O₄, V₂O₅, Cr₂O₅, or MnO₂can be used.

Alternatively, a complex material (LiMPO₄ (general formula) (M is one ormore of Fc(II), Mn(II), Co(II), and Ni(II))) can be used. Typicalexamples of the general formula LiMPO₄ which can be used as a materialare lithium compounds such as LiFePO₄, LiNiPO₄, LiCoPO₄, LiMnPO₄,LiFe_(a)Ni_(b)PO₄, LiFe_(a)Co_(b)PO₄, LiFe_(a)Mn_(b)PO₄,LiNi_(a)Co_(b)PO₄, LiNi_(a)Mn_(b)PO₄ (a+b≤1, 0<a<1, and 0<b<1),LiFe_(c)Ni_(a)Co_(e)PO₄, LiFe_(c)Ni_(d)Mn_(a)PO₄,LiNi_(c)Co_(d)Mn_(e)PO₄ (c+d+e≤1, 0<c<1, 0<d<1, and 0<e<1), andLiFe_(j)Ni_(g)Co_(h)Mn_(i)PO₄(f+g+h+i≤1, 0<f<1, 0<g<1, 0<h<1, and0<i<1).

Alternatively, a complex material such as Li_((2-f))MSiO₄ (generalformula) (M is one or more of Fe(II), Mn(II), Co(II), and Ni(II); 0≤j>2)may be used. Typical examples of the general formula Li_((2-j))MSiO₄which can be used as a material are lithium compounds such asLi_((2-f))FeSiO₄, Li_((2-j))NiSiO₄, Li_((2-j))CoSiO₄, Li_((2-j))MnSiO₄,Li_((2-j))Fe_(k)Ni_(l)SiO₄, Li_((2-j))Fe_(k)Co_(l)SiO₄,Li_((2-j))Fe_(k)Mn_(l)SiO₄, Li_((2-j))Ni_(k)Co_(l)SiO₄,Li_((2-j))Ni_(k)Mn_(l)SiO₄(k+l≤1, 0<k<1, and 0<l<1),Li_((2-j))Fe_(m)Ni_(n)Co_(q)SiO₄, Li_((2-j))Fe_(m)Ni_(n)Mn_(q)SiO₄,Li_((2-f))Ni_(m)Co_(n)Mn_(q)SiO₄ (m+n+q≤1, 0<m<1, 0<n<1, and 0<q<1), andLi_((2-j))Fe_(r)Ni_(s)Co_(t)Mn_(u)SiO₄ (r+s+t+u≤1, 0<r<1, 0<s<1, 0<t<1,and 0<u<1).

Still alternatively, a nasicon compound expressed by A_(x)M₂(XO₄)₃(general formula) (A═Li, Na, or Mg, M═Fe, Mn, Ti, V, Nb, or Al, X═S, P,Mo, W, As, or Si) can be used for the positive electrode activematerial. Examples of the nasicon compound are Fe₂(MnO₄)₃, Fe₂(SO₄)₃,and Li₃Fe₂(PO₄)₃. Further alternatively, a compound expressed byLi₂MPO₄F, Li₂MP₂O₇, or Li₅MO₄ (general formula) (M═Fe or Mn), aperovskite fluoride such as NaF₃ and FeF₃, a metal chalcogenide (asulfide, a selenide, or a telluride) such as TiS₂ and MoS₂, an oxidewith an inverse spinel structure such as LiMVO₄, a vanadium oxide (V₂O₅,V₆O₁₃, LiV₃O₈, or the like), a manganese oxide, an organic sulfur, orthe like can be used as the positive electrode active material.

In the case where carrier ions are alkali metal ions other than lithiumions, or alkaline-earth metal ions, a material containing an alkalimetal (e.g., sodium and potassium) or an alkaline-earth metal (e.g.,calcium, strontium, barium, beryllium, and magnesium) instead of lithiummay be used as the positive electrode active material.

As the separator 13, an insulator such as cellulose (paper),polyethylene with pores, and polypropylene with pores can be used.

As an electrolyte of an electrolytic solution, a material that containscarrier ions is used. Typical examples of the electrolyte are lithiumsalts such as LiPF₆, LiClO₄, LiAsF₆, LiBF₄, LiCF₃SO₃, Li(CF₃SO₂)₂N, andLi(C₂F₅SO₂)₂N. One of these electrolytes may be used alone, or two ormore of them may be used in an appropriate combination and in anappropriate ratio.

As a solvent of the electrolytic solution, a material with the carrierion mobility is used. As the solvent of the electrolytic solution, anaprotic organic solvent is preferably used. Typical examples of aproticorganic solvents include ethylene carbonate (EC), propylene carbonate,dimethyl carbonate, diethyl carbonate (DEC), γ-butyrolactone,acetonitrile, dimethoxyethane, tetrahydrofuran, and the like, and one ormore of these materials can be used. When a gelled high-molecularmaterial is used as the solvent of the electrolytic solution, safetyagainst liquid leakage and the like is improved. Furthermore, thestorage battery can be thinner and more lightweight. Typical examples ofgelled high-molecular materials include a silicone gel, an acrylic gel,an acrylonitrile gel, polyethylene oxide, polypropylene oxide, afluorine-based polymer, and the like. Alternatively, the use of one ormore kinds of ionic liquids (room temperature molten salts) which havefeatures of non-flammability and non-volatility as a solvent of theelectrolytic solution can prevent the storage battery from exploding orcatching fire even when the storage battery internally shorts out or theinternal temperature increases owing to overcharging and others. Anionic liquid is a salt in the liquid state and has high ion mobility(conductivity). An ionic liquid contains a cation and an anion. Examplesof ionic liquids include an ionic liquid containing anethylmethylimidazolium (EMI) cation and an ionic liquid containing anN-methyl-N-propylpiperidinium (PP₁₃) cation.

Instead of the electrolytic solution, a solid electrolyte including aninorganic material such as a sulfide-based inorganic material or anoxide-based inorganic material, or a solid electrolyte including amacromolecular material such as a polyethylene oxide (PEO)-basedmacromolecular material may alternatively be used. When the solidelectrolyte is used, a separator and a spacer are not necessary.Furthermore, the battery can be entirely solidified; therefore, there isno possibility of liquid leakage and thus the safety of the battery isdramatically increased.

A material with which lithium can be dissolved and precipitated or amaterial into and from which lithium ions can be inserted and extractedcan be used for a negative electrode active material of the negativeelectrode active material layer 19; for example, a lithium metal, acarbon-based material, an alloy-based material, or the like can be used.

The lithium metal is preferable because of its low redox potential(3.045 V lower than that of a standard hydrogen electrode) and highspecific capacity per unit weight and per unit volume (3860 mAh/g and2062 mAh/cm³).

Examples of the carbon-based material include graphite, graphitizingcarbon (soft carbon), non-graphitizing carbon (hard carbon), a carbonnanotube, graphene, carbon black, and the like.

Examples of the graphite include artificial graphite such as meso-carbonmicrobeads (MCMB), coke-based artificial graphite, or pitch-basedartificial graphite and natural graphite such as spherical naturalgraphite.

Graphite has a low potential substantially equal to that of a lithiummetal (0.1 V to 0.3 V vs. Li/Li⁺) when lithium ions are intercalatedinto the graphite (while a lithium-graphite intercalation compound isformed). For this reason, a lithium-ion secondary battery can have ahigh operating voltage. In addition, graphite is preferable because ofits advantages such as relatively high capacity per unit volume, smallvolume expansion, low cost, and safety greater than that of a lithiummetal.

For the negative electrode active material, an alloy-based materialwhich enables charge-discharge reactions by an alloying reaction and adealloying reaction with lithium can be used. In the case where carrierions are lithium ions, a material containing at least one of Al, Si, Ge,Sn, Pb, Sb, Bi, Ag, Au, Zn, Cd, In, Ga, and the like can be used as suchan alloy-based material, for example. Such elements have higher capacitythan carbon. In particular, silicon has a significantly high theoreticalcapacity of 4200 mAh/g. For this reason, silicon is preferably used asthe negative electrode active material. Examples of the material usingsuch elements include SiO, Mg₂Si, Mg₂Ge, SnO, SnO₂, Mg₂Sn, SnS₂, V₂Sn₃,FeSn₂, CoSn₂, Ni₃Sn₂, Cu₆Sn₅, Ag₃Sn, Ag₃Sb, Ni₂MnSb, CeSb₃, LaSn₃,La₃Co₂Sn₇, CoSb₃, InSb, SbSn, and the like. Note that SiO refers to thepowder of a silicon oxide including a silicon-rich portion and can alsobe referred to as SiO_(y) (2>y>0). Examples of SiO include a materialcontaining one or more of Si₂O₃, Si₃O₄, and Si₂O and a mixture of Sipowder and silicon dioxide (SiO₂). Furthermore, SiO may contain anotherelement (e.g., carbon, nitrogen, iron, aluminum, copper, titanium,calcium, and manganese). In other words, SiO refers to a coloredmaterial containing two or more of single crystal silicon, amorphoussilicon, polycrystal silicon, Si₂O₃, Si₃O₄, Si₂O, and SiO₂. Thus, SiOcan be distinguished from SiO_(x) (x is 2 or more), which is clear andcolorless or white. Note that in the case where a secondary battery isfabricated using SiO as a material thereof and the SiO is oxidizedbecause of repeated charge and discharge cycles, SiO is changed intoSiO₂ in some cases.

Alternatively, for the negative electrode active materials, an oxidesuch as titanium dioxide (TiO₂), lithium titanium oxide (Li₄Ti₅O₁₂),lithium-graphite intercalation compound (Li_(x)C₆), niobium pentoxide(Nb₂O₅), tungsten oxide (WO₂), or molybdenum oxide (MoO₂) can be used.

Still alternatively, for the negative electrode active materials,Li_(3-x)M_(x)N (M═Co, Ni, or Cu) with a Li₃N structure, which is anitride containing lithium and a transition metal, can be used. Forexample, Li_(2.6)Co_(0.4)N₃ is preferable because of high charge anddischarge capacity (900 mAh/g and 1890 mAh/cm³).

A nitride containing lithium and a transition metal is preferably used,in which case lithium ions are contained in the negative electrodeactive materials and thus the negative electrode active materials can beused in combination with a material for a positive electrode activematerial which does not contain lithium ions, such as V₂O₅ or Cr₃O₈. Inthe case of using a material containing lithium ions as a positiveelectrode active material, the nitride containing lithium and atransition metal can be used for the negative electrode active materialby extracting the lithium ions contained in the positive electrodeactive material in advance.

Alternatively, a material which causes a conversion reaction can be usedfor the negative electrode active materials; for example, a transitionmetal oxide which does not cause an alloy reaction with lithium, such ascobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may beused. Other examples of the material which causes a conversion reactioninclude oxides such as Fe₂O₃, CuO, Cu₂O, RuO₂, and Cr₂O₃, sulfides suchas CoS_(0.89,) NiS, and CuS, nitrides such as Zn₃N₂, Cu₃N, and Gc₃N₄,phosphides such as NiP₂, FeP₂, and CoP₃, and fluorides such as FeF₃ andBiF₃. Note that any of the fluorides can be used as a positive electrodeactive material because of its high potential.

The negative electrode active material layer 19 may further include abinder for increasing adhesion of active materials, a conductiveadditive for increasing the conductivity of the negative electrodeactive material layer 19, and the like in addition to the above negativeelectrode active materials.

In the secondary battery, for example, the separator 13 has a thicknessof approximately 25 μm, the positive electrode current collector 12 hasa thickness of approximately 20 μm to 40 μm, the positive electrodeactive material layer 18 has a thickness of approximately 100 μm, thenegative electrode active material layer 19 has a thickness ofapproximately 100 μm, and the negative electrode current collector 14has a thickness of approximately 20 μm to 40 μm. The film 11 has athickness of 0.113 mm. The film 11 is embossed to a depth ofapproximately 500 μm. If the film 11 is embossed to a depth of 2 mm ormore, the whole secondary battery is too thick; thus, the film 11 isembossed to a depth of 1 mm or less, preferably 500 μm or less. Althoughthe adhesive layer 30 is only partly illustrated in FIG. 2E, only athermocompression-bonded portion of a layer made of polypropylene whichis provided on the surface of the film 11 is the adhesive layer 30.

FIG. 2E illustrates an example where the bottom side of the film 11 isfixed and pressure bonding is performed. In this case, the top side isgreatly bent and a step is formed. Thus, when a plurality ofcombinations of the above stacked layers (e.g., eight or morecombinations) is provided inside the folded film 11, the step is largeand the top side of the film 11 might be too stressed. Furthermore, anend face of the top side of the film might be misaligned with an endface of the bottom side of the film. To prevent misalignment of the endfaces, a step may also be provided for the bottom side of the film andpressure bonding may be performed so that the thermocompression-bondedregion 17 is positioned at a center portion in the thickness directionof the secondary battery, whereby stress is uniformly applied.

Here, a current flow in charging a secondary battery will be describedwith reference to FIG. 2F. When a secondary battery using lithium isregarded as a closed circuit, lithium ions transfer and a current flowsin the same direction. Note that in the secondary battery using lithium,an anode and a cathode change places in charge and discharge, and anoxidation reaction and a reduction reaction occur on the correspondingsides; hence, an electrode with a high redox potential is called apositive electrode and an electrode with a low redox potential is calleda negative electrode. For this reason, in this specification, thepositive electrode is referred to as a “positive electrode” and thenegative electrode is referred to as a “negative electrode” in all thecases where charge is performed, discharge is performed, a reverse pulsecurrent is supplied, and a charging current is supplied. The use of theterms “anode” and “cathode” related to an oxidation reaction and areduction reaction might cause confusion because the anode and thecathode change places at the time of charging and discharging. Thus, theterms “anode” and “cathode” are not used in this specification. If theterm “anode” or “cathode” is used, it should be mentioned that the anodeor the cathode is which of the one at the time of charging or the one atthe time of discharging and corresponds to which of a positive electrodeor a negative electrode.

Two terminals in FIG. 2F are connected to a charger, and a secondarybattery 40 is charged. As the charge of the secondary battery 40proceeds, a potential difference between electrodes increases. Thepositive direction in. FIG. 2F is the direction in which a current flowsfrom one terminal outside the secondary battery 40 to the positiveelectrode current collector 12, flows from the positive electrodecurrent collector 12 to the negative electrode current collector 14 inthe secondary battery 40, and flows from the negative electrode currentcollector 14 to the other terminal outside the secondary battery 40. Inother words, a current flows in the direction of a flow of a chargingcurrent.

Although an example of a small battery used in a portable informationterminal or the like is described in this embodiment, one embodiment ofthe present invention is not particularly limited to this example.Application to a large battery provided in a vehicle or the like is alsopossible.

Although an example of application to a lithium-ion secondary battery isdescribed in this embodiment, one embodiment of the present invention isnot limited to this example. Application to a variety of secondarybatteries such as a lead storage battery, a lithium-ion polymersecondary battery, a nickel-hydrogen storage battery, a nickel-cadmiumstorage battery, a nickel-iron storage battery, a nickel-zinc storagebattery, a silver oxide-zinc storage battery, a solid-state battery, andan air battery is also possible. Application to a variety of powerstorage devices such as a primary battery, a capacitor, and alithium-ion capacitor is also possible. Furthermore, application to asolar cell, an optical sensor, a touch sensor, a display device, aflexible printed circuit (FPC), an optical film (e.g., a polarizingplate, a retardation plate, a prism sheet, a light reflective sheet, anda light diffusion sheet), and the like is also possible.

Embodiment 2

In this embodiment, an example where a plurality of combinations ofstacked layers that are partly different from those in Embodiment 1 isprovided inside the folded film 11 will be described.

FIG. 4A is a top view of the positive electrode current collector 12.FIG. 4B is a top view of the negative electrode current collector 14.FIG. 4C is a top view of the separator 13. FIG. 4D is a top view of thelead electrode 16. FIG. 4E is a top view of the film 11.

The dimensions of the positive electrode current collector, the negativeelectrode current collector, and the separator are substantially thesame in FIGS. 4A to 4C. A region 21 surrounded by a chain line in FIG.4E has substantially the same dimensions as the separator in FIG. 4C. Aregion between a dotted line and an end face in FIG. 4E is thethermocompression-bonded region 17.

FIG. 5A is a perspective view of two combinations of pairs of a positiveelectrode and a negative electrode. Note that an example where thepositive electrode current collector 12 is sandwiched between a positiveelectrode active material layers is illustrated. Specifically, thenegative electrode current collector 14, a negative electrode activematerial layer, the separator 13, a positive electrode active materiallayer, the positive electrode current collector 12, a positive electrodeactive material layer, the separator, a negative electrode activematerial layer, the negative electrode current collector are stacked inthis order. Although two separators are illustrated in FIG. 5A, oneseparator may be folded and the positive electrode current collector 12may be placed inside the folded separator.

The negative electrode current collector may be sandwiched betweennegative electrode active material layers. FIG. 5B illustrates anexample where three negative electrode current collectors eachsandwiched between negative electrode active material layers, fourpositive electrode current collectors each sandwiched between positiveelectrode active material layers, and eight separators are sandwichedbetween two negative electrode current collectors each having onesurface that is provided with a negative electrode active materiallayer.

In the case of thus stacking layers, four positive electrode currentcollectors are all fixed and electrically connected at a time byultrasonic welding. Furthermore, when ultrasonic welding is performedwith the four positive electrode current collectors overlapping with alead electrode, they can be electrically connected efficiently.

A protruding portion of a positive electrode current collector is alsocalled a tab portion. Ultrasonic welding can be performed in such amanner that ultrasonic waves are emitted to the tab portion of thepositive electrode current collector placed so as to overlap with a tabportion of another positive electrode current collector, while pressureis applied thereto.

The tab portion is likely to be cracked or cut by stress due to externalforce applied after fabrication of a secondary battery.

Thus, an ultrasonic welding apparatus including bonding dies illustratedin FIG. 6A is used in this embodiment. Note that only top and bottombonding dies of the ultrasonic welding apparatus are illustrated in FIG.6A for simplicity.

Tab portions of four positive electrode current collectors 12 and a leadelectrode are positioned between a first bonding die 22 provided withprojections 24 and a second bonding die 23. When ultrasonic welding isperformed with a region that needs to be welded overlapping with theprojections 24 and pressure is applied, a bent portion 25 is formed inthe tab portion between a welded region 26 and a region of the tabportion protruding from an end portion of the separator 13, asillustrated in FIG. 6B.

This bent portion 25 can relieve stress due to external force appliedafter fabrication of a secondary battery. Such a structure as canrelieve a strain caused by stress can prevent the secondary battery(e.g., an exterior body) from being damaged when changed in form bybeing bent, for example, achieving long-time reliability.

Furthermore, the ultrasonic welding apparatus including the bonding diesillustrated in FIG. 6A can perform ultrasonic welding and form the bentportion 25 at a time; thus, a secondary battery can be fabricatedwithout increasing the number of fabricating steps. Note that ultrasonicwelding and forming the bent portion 25 may be separately performed.

In addition, tab portions of five negative electrode current collectorsare also all welded to be electrically connected by ultrasonic weldingdescribed above.

The bent portion 25 is not necessarily formed in the tab portion. Torelieve stress, the shape of the tab portion of the positive electrodecurrent collector may be modified. Such a structure as can relieve astrain caused by stress can prevent the secondary battery (e.g., anexterior body) from being damaged when changed in form by being bent,for example, achieving long-time reliability.

FIG. 7A illustrates an example of a top view of a positive electrodecurrent collector 12 a as a modification example. A tab portion of thepositive electrode current collector 12 a may be provided with slits 27so that stress due to external force applied after fabrication of asecondary battery can be relieved. Such a structure as can relieve astrain caused by stress can prevent the secondary battery (e.g., anexterior body) from being damaged when changed in form by being bent,for example, achieving long-time reliability.

FIG. 7B illustrates an example of a top view of a positive electrodecurrent collector 12 b as another modification example. A corner of aregion 28, which is surrounded by a dotted line, of a tab portion of thepositive electrode current collector 12 b is rounded off to relieveconcentration of stress. Furthermore, the corner of the region 28 ispreferably more rounded off than the other corners to have a largeradius of curvature.

Alternatively, a high-strength material such as stainless steel may beused for a positive electrode current collector and the positiveelectrode current collector may be formed to have 10 μm or less, inorder to relieve stress due to external force applied after fabricationof a secondary battery.

It is needless to say that two or more of the above examples may becombined to relieve concentration of stress in the tab portion.

Note that this embodiment can be combined with Embodiment 1.

Embodiment 3

In this embodiment, an experiment where a secondary battery isfabricated and repetitively bent with a radius of curvature of 40 mm to150 mm inclusive will be described. It is found that the repetitivelybending the secondary battery with a radius of curvature of 40 mm to 150mm inclusive causes no problem.

First, a secondary battery is fabricated using the embossed film 10according to Embodiment 1.

In this embodiment, six combinations in each of which the positiveelectrode current collector 12, the separator 13, and the negativeelectrode current collector 14 are stacked as illustrated in FIG. 8A areused and wrapped with an exterior film. A positive electrode having onesurface provided with a positive electrode active material layer and anegative electrode having one surface provided with a negative electrodeactive material layer are used. Specifically, the positive electrodehaving one surface provided with the positive electrode active materiallayer, the separator to be in contact with the positive electrode activematerial layer, the negative electrode having one surface provided withthe negative electrode active material layer that is to be in contactwith the separator, and the negative electrode current collector to bein contact with the negative electrode active material layer are stackedin this order. Although 12 separators are illustrated in FIG. 8B, onlysix separators are used in the case where one separator is folded andthe positive electrode current collector 12 is placed inside the foldedseparator.

According to Embodiment 2, six positive electrode current collectors anda lead electrode are welded by ultrasonic welding with the use of anultrasonic welding apparatus including the bonding dies illustrated inFIG. 6A. In addition, six negative electrode current collectors and alead electrode are welded by ultrasonic welding.

Then, the outer edge of the exterior film except a part for introducingan electrolytic solution is subjected to thermocompression bondingaccording to Embodiment 1, a predetermined amount of electrolyticsolution is introduced into a space surrounded by the film in an inertatmosphere, and the part of the outer edge of the exterior film that hasnot yet been subjected to thermocompression bonding and is left open issealed by thermocompression bonding. The thickness of a thickest portionof the lithium-ion secondary battery obtained in this manner (the totalthickness including the thickness of an exterior body) is approximately3 mm.

FIG. 9A is a photograph taken while the lithium-ion secondary battery isbent. FIG. 9B is a schematic view thereof. A bending test of thelithium-ion secondary battery is performed, and it is confirmed thatbending the secondary battery with a radius of curvature of 40 mm to 150mm inclusive 10000 times causes no problem and the secondary battery canbe charged and discharged. It is needless to say that an external bodyand the like are not damaged and leakage or the like of an electrolyticsolution and the like does not occur. The film serving as the exteriorbody has a surface provided with a plurality of projections anddepressions; thus, wrinkles are not easily formed and concentration ofstress is suppressed when the secondary battery is changed in form bybeing bent. This helps prevent damage to the film. In the case where thefilm does not have a surface provided with a plurality of projectionsand depressions, large wrinkles are concentrated at a bent portion whenthe secondary battery is changed in form by being bent. As a result, ahole might be formed and an electrolytic solution might leak out, or aportion of an adhesive layer at which the wrinkles are concentratedmight be damaged and an electrolytic solution might leak out from acrack formed in the adhesive layer.

FIG. 10A is an X-ray CT image of a cross section of an end portion ofthe obtained lithium-ion secondary battery observed by an X-ray CTscanner after the lithium-ion secondary battery is bent with a radius ofcurvature of 40 mm to 150 mm inclusive 10000 times. FIG. 10B is aschematic view thereof. In FIG. 10A, a portion damaged by bending thesecondary battery 10000 times is not found, which implies that chargeand discharge can be performed without any problem. Note that an X-rayCT scanner is an apparatus in which a subject is exposed to X-rays andthe X-rays transmitted through or scattered by the subject are detectedby an X-ray detector, and a tomographic image of the subject is obtainedon the basis of the X-ray detection output (the number of photons of theX-rays). With the X-ray CT scanner, a cross section of a secondarybattery can be observed nondestructively.

In FIG. 10A, the exterior film 11, the positive electrode currentcollector 12, the negative electrode current collector 14 are made ofmetal materials and do not transmit X-rays. This allows a cleartomographic image of them in the secondary battery to be obtained. Incontrast, the separator, the positive electrode active material layer,and the negative electrode active material layer transmit X-rays, and itis difficult to identify them in FIG. 10B.

It is also observed by the X-ray CT scanner that unevenness of a surfaceof the film is changed and stress is sufficiently relieved when thelithium-ion secondary battery is bent. Such a structure as can relieve astrain caused by stress can prevent the secondary battery (e.g., anexterior body) from being damaged when changed in form by being bent,for example, achieving long-time reliability.

Embodiment 4

In this embodiment, examples of electronic devices incorporating any ofthe lithium-ion secondary batteries described in Embodiments 1 to 3 willbe described.

The secondary battery fabricated according to any of Embodiments 1 to 3includes, as an exterior body, a thin film having flexibility, and thuscan be attached to a support structure body with a curved surface bychanging its form along the curved surface of the support structurebody.

Next, a display module to be attached to the secondary battery isprepared. The display module refers to a display panel provided with atleast an FPC. FIG. 11A is a cross-sectional schematic view of anelectronic device. The electronic device in FIG. 11A includes a displayportion 102, an FPC, and a driver circuit and preferably furtherincludes a converter for power feeding from a secondary battery 103. Thesupport structure body 101 is in the form of a bracelet obtained bycurving a band-like structure body. At least part of the supportstructure body 101 has flexibility and can be moved in the direction ofarrows 105; thus, the electronic device can be put around a wrist.

In the display module, the display portion 102 is flexible and a displayelement is provided over a soft and flexible film. Examples of the softand flexible film include a plastic film containing an organic materialand an inorganic film containing an inorganic material. As an inorganicfilm, glass with a thickness small enough to have flexibility,specifically, a thickness of 20 μm to 200 μm inclusive, preferably 25 μmto 100 μm inclusive is used. Examples of glass include non-alkali glass,barium borosilicate glass, and aluminoborosilicate glass. When glass isused as the flexible film, a barrier property against water and oxygencan be improved, so that the lifetime of an organic EL element can beincreased and a reliable light-emitting panel can be provided.Alternatively, a substrate in which a glass fiber is impregnated with anorganic resin or a substrate whose thermal expansion coefficient isreduced by mixing an organic resin with an inorganic filler may be used.A substrate using such a material is lightweight, and thus alight-emitting panel using this substrate can also be lightweight. Thesecondary battery 103 and the display portion 102 are preferablydisposed so as to partly overlap with each other. When the secondarybattery 103 and the display portion 102 are disposed so as to partly orentirely overlap with each other, the electrical path, i.e., the lengthof a wiring, from the secondary battery 103 to the display portion canbe shortened, whereby power consumption can be reduced.

Examples of methods for forming the display element over the flexiblefilm include a method in which the display element is directly formedover the flexible film; a method in which a layer including the displayelement is formed over a rigid substrate such as a glass substrate, thesubstrate is removed by etching, polishing, or the like, and then thelayer including the display element and the flexible film are attachedto each other; and a method in which a separation layer is provided overa rigid substrate such as a glass substrate, a layer including thedisplay element is formed thereover, the rigid substrate and the layerincluding the display element are separated from each other using theseparation layer, and then the layer including the display element andthe flexible film are attached to each other. Examples of the separationlayer include a metal oxide film such as a tungsten oxide film, anorganic resin film such as a polyimide film, and an amorphous siliconfilm. In the case of using an organic resin film such as a polyimidefilm or an amorphous silicon film as the separation layer, separation isperformed in such a manner that ablation is caused by irradiation withlaser light.

FIG. 11B is a photograph of an electronic device that can display animage on a display portion. The electronic device shown in FIG. 11B islight when worn on an arm (e.g., a forearm). In addition, the electronicdevice presents an appearance with an attractive design and can thusalso be used as an accessory.

FIG. 12A is a photograph of a side surface of an electronic device. FIG.12B is a photograph of the electronic device taken so that the secondarybattery can be seen. As in FIG. 12B, the electronic device includes alight-transmitting plastic substrate as the support structure body 101and thus the secondary battery 103 can be visually recognized from theback surface side of the electronic device and a surface of an embossedfilm can be observed.

The electronic device illustrated in FIG. 12A includes the supportstructure body 101, the secondary battery 103, a control board 107, anda cover 104. The control board 107 is an insulating wiring board onwhich a semiconductor element, a resistor, a capacitor, and the like aremounted. The insulating wiring board is formed by binding ceramic powderof aluminum oxide, silicon oxide, calcium oxide, or the like with anorganic polymer material. Specifically, the secondary battery 103, thecontrol board 107, and the cover 104 are provided in this order over thesupport structure body 101. In addition, the electronic device isprovided with an antenna (not shown) for wireless charging, and thewireless charging can be performed according to the Qi standard.

The support structure body 101 is flexible and thus can be easily bent.Note that a material other than plastic can be used for the supportstructure body 101.

The control board 107 has slits to bend it, and is provided with acommunication device conforming to Bluetooth (registered trademark, thesame as IEEE802.15.1) standards, a microcomputer, a storage device, anFPGA, a DA converter, a charge control IC, a level shifter, and thelike. In addition, the control board 107 is connected to a displaymodule including a display portion through an input/output connector.

In addition, the display portion may be provided with a touch panel sothat input of data to the electronic device and operation of theelectronic device can be performed with the touch panel. The displayportion may have a structure where a first film is provided with alight-emitting element, a second film is provided with a touch sensor,the second film serves as a sealing plate, and the first film and thesecond film are bonded with the light-emitting element and the touchsensor positioned therebetween. In the case of providing a touch panelseparately from the display portion, the touch panel is formed byproviding a touch sensor over a bendable film. In addition, a bufferlayer such as a resin layer may be provided between the touch panel andthe display portion. To protect the touch panel from being damaged, asurface of the touch panel may be provided with a protective layer suchas a protective film or a resin layer.

FIG. 17A is a photograph showing the state where a user wears anelectronic device on his or her arm. A display portion is an activematrix display device and includes a transistor including an oxidesemiconductor layer and an organic EL element electrically connected tothe transistor. The electronic device has a good design as in FIG. 17Aand thus can be used as an accessory. FIG. 17B is a photograph of theelectronic device taken from the back side thereof. FIG. 17C is aphotograph of the electronic device that is changed in form by hand.

FIG. 18 is a structural schematic diagram of a side surface of theelectronic device and is an enlarged schematic diagram of the photographin FIG. 12A.

The electronic device in FIG. 18 includes the support structure body101, the secondary battery 103, the control board 107, the displayportion 102, a protective member 813, and a cover 812. Specifically, thesecondary battery 103, the control board 107, and the protective member813 whose thickness is approximately one third of the thickness of thesupport structure body 101, and the display portion 102 and the cover812 are provided in this order over the support structure body 101. Inaddition, the electronic device is provided with an antenna 815 forwireless charging, and the wireless charging can be performed accordingto the Qi standard. The electronic device includes a communicationdevice 817 for wirelessly communicating data to be used to performdisplay with an external device.

The secondary battery 103 fabricated according to Embodiment 1 includes,as an exterior body, a thin flexible film that is embossed. Thesecondary battery 103 is provided over the support structure body 101having a curved surface (may be bonded to the support structure body 101having a curved surface) and can change its form along the curvedsurface of a region of the support structure body 101 that has a largeradius of curvature.

The support structure body 101 is flexible and thus can be easily bent.Note that a material other than plastic can also be used for the supportstructure body 101. The support structure body 101 is in the form of abracelet obtained by curving a band-like structure body. The supportstructure body 101 may have a cross-sectional shape with a uniformradius of curvature but preferably has a cross-sectional shape withdifferent radii of curvature because the electronic device is worn on anarm. In the cross section of the support structure body 101, a regionwith a large radius of curvature, that is, a region overlapping with thedisplay portion is sandwiched between two regions with a small radius ofcurvature as illustrated in FIG. 18 . Thus, the support structure body101 has a cross-sectional shape that fits a forearm (the cross-sectionalshape of the support structure body 101 is an ellipse). In addition, thesupport structure body 101 is partly flexible, and the electronic devicecan be worn on a wrist while the support structure body 101 is changedin form. When the form of the electronic device is changed, misalignmentbetween the support structure body 101 and the display portion 102 orbetween the support structure body 101 and the protective member 813might occur. Even if misalignment occurs because of the charge in form,neither the display portion 102 nor the support structure body 101 isfixed and the protective member 813 keeps a space to prevent the controlboard 107 and the display portion 102 from being in contact with eachother. That is, an air buffer layer is provided as a buffer layerbetween the control board 107 and the protective member 813.Furthermore, a sealant that is in contact with the support structurebody is preferably provided to prevent entry of water and dust from aside surface of the electronic device. This sealant preferably preventsentry of water and dust when the electronic device is changed in form,and thus is preferably made of a flexible material (an elastic resinsuch as a polyurethane resin, an acrylic resin, a silicone resin, anepoxy resin, and a resin containing polybutadiene as a main component).

The protective member 813 protects a component inside the electronicdevice, in particular, the control board 107 from a sudden shock. Theprotective member 813 has an opening for passing the FPC 819therethrough, and also serves as a support body of the display portionto maintain the curvature of a display screen because the displayportion is thin. The protective member 813 can change its form as a partof the electronic device and thus can be made of a material similar tothat of the support structure body 101. Note that the protective member813 may be made of a material different from that of the supportstructure body 101.

The cover 812 is a light-blocking film having one surface coated with anadhesive and covers part of the electronic device to bring componentstogether and has an opening overlapping with the display portion 102.The cover 812 can conceal the internal structure owing to itslight-blocking property, improving the design of the electronic device.Note that the electronic device may be intentionally formed so that itsinternal structure can be seen externally. In that case, the cover 812does not have to have a light-blocking property. Also in the case wherethe protective member 813 has a light-blocking property, the cover 812does not have to have a light-blocking property.

The control board 107 has slits to bend it, and is provided with thecommunication device 817 conforming to Bluetooth (registered trademark,the same as IEEE802.15.1) standards, a microcomputer, a storage device,an FPGA, a DA converter, a charge control IC, a level shifter, and thelike. ICs 820 a, 820 b, and 820 c (e.g., a microcomputer, a storagedevice, an FPGA, a DA converter, a charge control IC, and a levelshifter) and the like are mounted on flat surfaces each of which isbetween the slits of the control board 107 as illustrated in FIG. 18 .The control board 107 is connected to a display module including thedisplay portion 102 through an input/output connector 814. In addition,the control board 107 is connected to the antenna 815 through a wiring818 and connected to the secondary battery 103 through a lead electrode803 and a connection portion 810. A power supply control circuit 816controls charge and discharge of the secondary battery 103.

The display module refers to a display panel provided with at least anFPC 819. The electronic device in FIG. 18 includes the display portion102, the FPC 819, and a driver circuit and further includes a converterfor power feeding from the secondary battery 103.

The secondary battery 103 and the display portion 102 are preferablydisposed so as to partly overlap with each other. When the secondarybattery 103 and the display portion 102 are disposed so as to partly orentirely overlap with each other, the electrical path, i.e., the lengthof a wiring, from the secondary battery 103 to the display portion 102can be shortened, whereby power consumption can be reduced. In addition,providing the display module between the protective member 813 and thecover 812 enables protection of the display module from unexpecteddeformation (e.g., wrinkles or a twist), increasing the lifetime of theelectronic device as a product.

FIGS. 13A to 13H illustrate examples of other electronic devices.

Examples of electronic devices each using a flexible power storagedevice are as follows: head-worn display devices such as head-mounteddisplays and goggle type displays, arm-worn display devices, stationarydisplay devices (also referred to as televisions or televisionreceivers), desktop personal computers, laptop personal computers,monitors for computers or the like, cameras such as digital cameras ordigital video cameras, digital photo frames, electronic notebooks,e-book readers, electronic translators, toys, audio input devices suchas microphones, electric shavers, electric toothbrushes, high-frequencyheating appliances such as microwave ovens, electric rice cookers,electric washing machines, electric vacuum cleaners, water heaters,electric fans, hair dryers, air-conditioning systems such ashumidifiers, dehumidifiers, and air conditioners, dishwashers, dishdryers, clothes dryers, futon dryers, electric refrigerators, electricfreezers, electric refrigerator-freezers, freezers for preserving DNA,flashlights, electric power tools, alarm devices such as smokedetectors, gas alarm devices, and security alarm devices, industrialrobots, health equipment and medical equipment such as hearing aids,cardiac pacemakers, X-ray equipment, radiation counters, electricmassagers, and dialyzers, mobile phones (also referred to as mobilephone devices or cell phones), portable game machines, portableinformation terminals, lighting devices, headphone stereos, stereos,remote controls, clocks such as table clocks and wall clocks, cordlessphone handsets, transceivers, pedometers, calculators, portable orstationary music reproduction devices such as digital audio players, andlarge game machines such as pachinko machines.

In addition, a flexible power storage device can be incorporated along acurved inside/outside wall surface of a house or a building or a curvedinterior/exterior surface of an automobile.

FIG. 13A illustrates an example of a mobile phone. A mobile phone 7400includes a display portion 7402 incorporated in a housing 7401, anoperation button 7403, an external connection port 7404, a speaker 7405,a microphone 7406, and the like. Note that the mobile phone 7400includes a power storage device 7407.

FIG. 13B illustrates the mobile phone 7400 that is bent. When the wholemobile phone 7400 is bent by external force, the power storage device7407 included in the mobile phone 7400 is also bent. FIG. 13Cillustrates the bent power storage device 7407. The power storage device7407 is a laminated storage battery (also referred to as a layeredbattery or a film-covered battery). The power storage device 7407 isfixed while being bent. Note that the power storage device 7407 includesa lead electrode 7408 electrically connected to a current collector7409. For example, a film serving as an exterior body of the powerstorage device 7407 is embossed, so that the power storage device 7407has high reliability even when bent. The mobile phone 7400 may furtherbe provided with a slot for insertion of a SIM card, a connector portionfor connecting a USB device such as a USB memory.

FIG. 130 illustrates an example of a mobile phone that can be bent. Whenbent to be put around a forearm, the mobile phone can be used as abangle-type mobile phone as in FIG. 13E. The bangle-type mobile phoneillustrated in FIG. 13E can also be referred to as an arm-worn displaydevice. A mobile phone 7100 includes a housing 7101, a display portion7102, an operation button 7103, and a power storage device 7104. FIG.13F illustrates the power storage device 7104 that can be bent. When themobile phone is worn on a user's arm while the power storage device 7104is bent, the housing changes its form and the curvature of a part or thewhole of the power storage device 7104 is changed. Specifically, a partor the whole of the housing or the main surface of the power storagedevice 7104 is changed in the range of radius of curvature from 10 mm to150 mm. Note that the power storage device 7104 includes a leadelectrode 7105 that is electrically connected to a current collector7106. For example, pressing is performed to form a plurality ofprojections and depressions on a surface of the film serving as theexterior body of the power storage device 7104, and retains highreliability even when the power storage device 7104 is bent many timeswith different curvatures. The mobile phone 7100 may further be providedwith a slot for insertion of a SIM card, a connector portion forconnecting a USB device such as a USB memory. When a center portion ofthe mobile phone illustrated in FIG. 13D is folded, a form illustratedin FIG. 13G can be obtained. When a center portion of the mobile phoneis further folded so that end portions of the mobile phone overlap witheach other as illustrated in FIG. 13H, the mobile phone can be reducedin size so as to be put in, for example, a pocket of clothes a userwears. As described above, the mobile phone illustrated in FIG. 13D canbe changed in form in more than one ways, and it is desirable that atleast the housing 7101, the display portion 7102, and the power storagedevice 7104 have flexibility in order to change the form of the mobilephone.

FIG. 16A illustrates an example of a vacuum cleaner. By being providedwith a secondary battery, the vacuum cleaner can be cordless. To securea dust collecting space for storing vacuumed dust inside the vacuumcleaner, a space occupied by a power storage device 7604 is preferablyas small as possible. For this reason, it is useful to provide the thinpower storage device 7604 that can be bent, between the outside surfaceand the dust collecting space.

The vacuum cleaner 7600 is provided with operation buttons 7603 and thepower storage device 7604. FIG. 16B illustrates the power storage device7604 that is capable of being bent. A film serving as an exterior bodyof the power storage device 7604 is embossed, so that the power storagedevice 7604 has high reliability even when bent. The power storagedevice 7604 includes a lead electrode 7601 electrically connected to anegative electrode and a lead electrode 7602 electrically connected to apositive electrode.

As another example of the power storage device 7604 where two leadelectrodes are exposed from one short side of an exterior body, thepower storage device 7605 that is capable of being bent is illustratedin FIG. 16C. The power storage device 7605 has a structure where acurrent collector and a lead electrode are exposed from two respectiveshort sides of an exterior body. A film serving as the exterior body ofthe power storage device 7605 may also be embossed, in which case thepower storage device 7605 can be bent and have high reliability.

FIG. 16D illustrates an example of the internal structure of the powerstorage device 7605. As illustrated in FIG. 16D, the power storagedevice 7605 includes the positive electrode current collector 12, theseparator 13, and two negative electrode current collectors 14. The twonegative electrode current collectors 14 have slits that extend in thedirection perpendicular to the direction in which the power storagedevice 7605 is bent. The separator 13 is folded and the positiveelectrode current collector 12 is provided inside the folded separator13. In addition, the positive electrode current collector 12 issandwiched between positive electrode active material layers.

The thin power storage device 7604 can be fabricated by the method forfabricating a laminated secondary battery that is described inEmbodiment 1 or 2.

The thin power storage device 7604 has a laminated structure and is bentand fixed. The vacuum cleaner 7600 includes a display portion 7606 thatdisplays, for example, the remaining amount of power in the thin powerstorage device 7604. A display area of the display portion 7606 iscurved to fit the shape of the outer surface of the vacuum cleaner. Thevacuum cleaner includes a connection cord for being connected to areceptacle. When the thin power storage device 7604 is charged to havesufficient power, the connection cord can be removed from the receptacleto use the vacuum cleaner. The thin power storage device 7604 may becharged wirelessly without using the connection cord.

The use of power storage devices that can be bent in vehicles enablesproduction of next-generation clean energy vehicles such as hybridelectric vehicles (HEVs), electric vehicles (EVs), and plug-in hybridelectric vehicles (PHEVs). Moreover, power storage devices that can bebent can also be used in moving objects such as agricultural machines,motorized bicycles including motor-assisted bicycles, motorcycles,electric wheelchairs, electric carts, boats or ships, submarines,aircrafts such as fixed-wing aircrafts and rotary-wing aircrafts,rockets, artificial satellites, space probes, planetary probes, andspacecrafts.

FIGS. 14A and 14B each illustrate an example of a vehicle fabricatedaccording to one embodiment of the present invention. An automobile 8100illustrated in FIG. 14A is an electric vehicle that runs on the power ofan electric motor 8106. Alternatively, the automobile 8100 is a hybridelectric vehicle capable of driving using either the electric motor 8106or the engine as appropriate. In the case of providing a laminatedsecondary battery in the vehicle, a battery module including a pluralityof laminated secondary batteries is placed in one place or more than oneplace. According to one embodiment of the present invention, a powerstorage device itself can be made more compact and lightweight, and forexample, when the power storage device having a curved surface isprovided on the inside of a tire of a vehicle, the vehicle can be ahigh-mileage vehicle. Furthermore, a power storage device that can havevarious shapes can be provided in a small space in a vehicle, whichallows a space in a trunk and a space for riders to be secured. Theautomobile 8100 includes the power storage device. The power storagedevice is used not only to drive the electric motor 8106, but also tosupply electric power to a light-emitting device such as a headlight8101 or a room light (not illustrated).

The power storage device can also supply electric power to a displaydevice of a speedometer, a tachometer, or the like included in theautomobile 8100. Furthermore, the power storage device can supplyelectric power to a semiconductor device included in the automobile8100, such as a navigation system.

FIG. 14B illustrates an automobile 8200 including the power storagedevice. The automobile 8200 can be charged when the power storage deviceis supplied with electric power through external charging equipment by aplug-in system, a contactless power feeding system, or the like. In FIG.14B, the power storage device included in the automobile 8200 is chargedwith the use of a ground-based charging apparatus 8021 through a cable8022. In charging, a given method such as CHAdeMO (registered trademark)or Combined Charging System may be employed as a charging method, thestandard of a connector, or the like as appropriate. The chargingapparatus 8021 may be a charging station provided in a commerce facilityor a power source in a house. For example, with the use of a plug-intechnique, the power storage device 8024 included in the automobile 8200can be charged by being supplied with electric power from outside. Thecharging can be performed by converting AC electric power into DCelectric power through a converter such as an AC-DC converter.

Furthermore, although not illustrated, the vehicle may include a powerreceiving device so that it can be charged by being supplied withelectric power from an above-ground power transmitting device in acontactless manner. In the case of the contactless power feeding system,by fitting a power transmitting device in a road or an exterior wall,charging can be performed not only when the electric vehicle is stoppedbut also when driven. In addition, the contactless power feeding systemmay be utilized to perform transmission and reception of electric powerbetween two vehicles. Furthermore, a solar cell may be provided in theexterior of the automobile to charge the power storage device when theautomobile stops or moves. To supply electric power in such acontactless manner, an electromagnetic induction method or a magneticresonance method can be used.

According to one embodiment of the present invention, the degree offlexibility in place where the power storage device can be provided isincreased and thus a vehicle can be designed efficiently. Furthermore,according to one embodiment of the present invention, the power storagedevice itself can be made more compact and lightweight as a result ofimproved characteristics of the power storage device. The compact andlightweight power storage device contributes to a reduction in theweight of a vehicle, and thus increases the driving distance.Furthermore, the power storage device included in the vehicle can beused as a power source for supplying electric power to products otherthan the vehicle. In such a case, the use of a commercial power sourcecan be avoided at peak time of electric power demand.

This embodiment can be freely combined with any one of Embodiments 1 to3.

Embodiment 5

As other examples of electronic devices using power storage devices,medical electronic devices that can acquire biological data will bedescribed. An electronic device 60 in FIGS. 15A and 15B can be formed insuch a manner that a housing 61 is provided with one or more of sensors,and thus has a function of measuring force, displacement, position,speed, acceleration, angular velocity, rotational frequency, distance,light, liquid, magnetism, temperature, chemical substance, sound, time,hardness, electric field, current, voltage, electric power, radiation,flow rate, humidity, gradient, oscillation, odor, or infrared rays. Withsensors 63 a and 63 b, for example, data on an environment (e.g.,temperature) where the power storage device is placed can be determinedand stored in a memory circuit 64. The housing 61 is provided with adisplay portion 62 that includes a touch input sensor.

For example, the electronic device 60 is provided with a light sourcesuch as an LED so that light from the light source can be emitted to askin overlapping with the electronic device 60 to measure a change inbloodstream from reflected light from the inside of the skin and acquirepulse data by arithmetic processing. Measurement is performed at morethan one portion and the average of the measurement results is used toacquire accurate biological data. The electronic device 60 is furtherprovided with a circuit 65 that can perform signal processing operationsuch as a CPU.

The electronic device 60 may be provided with a sensor that can acquirebiological data other than pulse data. Examples of other biological datainclude temperature, blood pressure, the amount of activity, the numberof steps taken, and the proportion of subcutaneous fat.

Although FIGS. 15A and 15B illustrate the electronic device includingthe display portion 62, one embodiment of the present invention is notparticularly limited thereto. Even without the display portion 62,acquired biological data can be checked by being displayed on anotherelectronic device such as a mobile phone or a smartphone when at least acircuit 66 (including an antenna, for example) that can send and receivebiological data is provided. In the case where a user who wears theelectronic device 60 on his or her arm is a person who requires nursingcare, it is preferable that data be sent also to medical facilities suchas a hospital in a remote location. In that case, data can be providedto the hospital in real time and the user can obtain directionsregarding a proper treatment from a doctor in the hospital, for example,with a mobile phone or a smartphone.

The electronic device 60 may have a function of acquiring currentbiological data of a user as well as positional data received by GPS ofthe electronic device 60 and automatically informing a medical facilityof the data urgently when he or she who wears the electronic device 60on his or her arm collapses on a road because of physical abnormality.When data of a donor card or data on a user's name, age, blood type, andthe like are stored in the circuit 64, a saver can obtain information onthe user by using the electronic device 60 even if he or she isunconscious.

This embodiment can be freely combined with any one of Embodiments 1 to4.

Note that what is described (or part thereof) in one embodiment can beapplied to, combined with, or replaced with different contents in theembodiment and/or what is described (or part thereof) in anotherembodiment or other embodiments.

Note that in each embodiment, what is described in the embodiment iscontents described with reference to a variety of diagrams or contentsdescribed with text described in this specification.

Note that by combining a diagram (or may be part of the diagram)illustrated in one embodiment with another part of the diagram, adifferent diagram (or may be part of the different diagram) illustratedin the embodiment, and/or a diagram (or may be part of the diagram)illustrated in another embodiment or other embodiments, much morediagrams can be formed.

Note that contents that are not specified in any drawing or text in thespecification can be excluded from one embodiment of the invention.Alternatively, when the range of a value that is defined by the maximumand minimum values is described, part of the range is appropriatelynarrowed and part of the range is removed, whereby one embodiment of theinvention can be constituted excluding part of the range can beconstructed. In this manner, it is possible to specify the technicalscope of one embodiment of the present invention so that a conventionaltechnology is excluded, for example.

As a specific example, a diagram of a circuit including first to fifthtransistors is illustrated. In that case, it can be specified that thecircuit does not include a sixth transistor in the invention. It can bespecified that the circuit does not include a capacitor in theinvention. It can be specified that the circuit does not include a sixthtransistor with a particular connection structure in the invention. Itcan be specified that the circuit does not include a capacitor with aparticular connection structure in the invention. For example, it can bespecified that a sixth transistor whose gate is connected to a gate ofthe third transistor is not included in the invention. For example, itcan be specified that a capacitor whose first electrode is connected tothe gate of the third transistor is not included in the invention.

As another specific example, the description of a value, “a voltage ispreferably higher than or equal to 3 V and lower than or equal to 10 V”is given. In that case, for example, it can be specified that the casewhere the voltage is higher than or equal to −2 V and lower than orequal to 1 V is excluded from one embodiment of the invention. Forexample, it can be specified that the case where the voltage is higherthan or equal to 13 V is excluded from one embodiment of the invention.Note that, for example, it can be specified that the voltage is higherthan or equal to 5 V and lower than or equal to 8 V in the invention.For example, it can be specified that the voltage is approximately 9 Vin the invention. For example, it can be specified that the voltage ishigher than or equal to 3 V and lower than or equal to 10 V but is not 9V in the invention. Note that even when the description “a value ispreferably in a certain range” or “a value preferably satisfies acertain condition” is given, the value is not limited to thedescription. In other words, a description of a value that includes aterm “preferable”, “preferably”, or the like does not necessarily limitthe value.

As another specific example, the description “a voltage is preferred tobe 10 V” is given. In that case, for example, it can be specified thatthe case where the voltage is higher than or equal to −2 V and lowerthan or equal to 1 V is excluded from one embodiment of the invention.For example, it can be specified that the case where the voltage ishigher than or equal to 13 V is excluded from one embodiment of theinvention.

As another specific example, the description “a film is an insulatingfilm” is given to describe a property of a material. In that case, forexample, it can be specified that the case where the insulating film isan organic insulating film is excluded from one embodiment of theinvention. For example, it can be specified that the case where theinsulating film is an inorganic insulating film is excluded from oneembodiment of the invention. For example, it can be specified that thecast where the insulating film is a conductive film is excluded from oneembodiment of the invention. For example, it can be specified that thecase where the insulating film is a semiconductor film is excluded fromone embodiment of the invention.

As another specific example, the description of a stacked structure, “afilm is provided between an A film and a B film” is given. In that case,for example, it can be specified that the case where the film is alayered film of four or more layers is excluded from the invention. Forexample, it can be specified that the case where a conductive film isprovided between the A film and the film is excluded from the invention.

Note that various people can implement one embodiment of the inventiondescribed in this specification and the like. However, different peoplemay be involved in the implementation of the embodiment of theinvention. For example, in the case of a transmission/reception system,the following case is possible: Company A manufactures and sellstransmitting devices, and Company B manufactures and sells receivingdevices. As another example, in the case of a light-emitting deviceincluding a transistor and a light-emitting element, the following caseis possible: Company A manufactures and sells semiconductor devicesincluding transistors, and Company B purchases the semiconductordevices, provides light-emitting elements for the semiconductor devices,and completes light-emitting devices.

In such a case, one embodiment of the invention can be constituted sothat a patent infringement can be claimed against each of Company A andCompany B. In other words, one embodiment of the invention can beconstituted so that only Company A implements the embodiment, andanother embodiment of the invention can be constituted so that onlyCompany B implements the embodiment. One embodiment of the inventionwith which a patent infringement suit can be filed against Company A orCompany B is clear and can be regarded as being disclosed in thisspecification or the like. For example, in the case of atransmission/reception system, even when this specification or the likedoes not include a description of the case where a transmitting deviceis used alone or the case where a receiving device is used alone, oneembodiment of the invention can be constituted by only the transmittingdevice and another embodiment of the invention can be constituted byonly the receiving device. Those embodiments of the invention are clearand can be regarded as being disclosed in this specification or thelike. Another example is as follows: in the case of a light-emittingdevice including a transistor and a light-emitting element, even whenthis specification or the like does not include a description of thecase where a semiconductor device including the transistor is used aloneor the case where a light-emitting device including the light-emittingelement is used alone, one embodiment of the invention can beconstituted by only the semiconductor device including the transistorand another embodiment of the invention can be constituted by only thelight-emitting device including the light-emitting element. Thoseembodiments of the invention are clear and can be regarded as beingdisclosed in this specification or the like.

Note that in this specification and the like, it may be possible forthose skilled in the art to constitute one embodiment of the inventioneven when portions to which all the terminals of an active element(e.g., a transistor or a-diode), a passive element (e.g., a capacitor ora resistor), are the like are connected are not specified. In otherwords, one embodiment of the invention is clear even when connectionportions are not specified. Further, in the case where a connectionportion is disclosed in this specification and the like, it can bedetermined that one embodiment of the invention in which a connectionportion is not specified is disclosed in this specification and thelike, in some cases. In particular, in the case where the number ofportions to which the terminal is connected may be more than one, it isnot necessary to specify the portions to which the terminal isconnected. Therefore, it may be possible to constitute one embodiment ofthe invention by specifying only portions to which some of terminals ofan active element (e.g., a transistor or a diode), a passive element(e.g., a capacitor or a resistor), and the like are connected.

Note that in this specification and the like, it may be possible forthose skilled in the art to specify the invention when at least theconnection portion of a circuit is specified. Alternatively, it may bepossible for those skilled in the art to specify the invention when atleast a function of a circuit is specified. In other words, when afunction of a circuit is specified, one embodiment of the presentinvention is clear. Moreover, it can be determined that one embodimentof the present invention whose function is specified is disclosed inthis specification and the like. Therefore, when a connection portion ofa circuit is specified, the circuit is disclosed as one embodiment ofthe invention even when a function is not specified, and one embodimentof the invention can be constituted. Alternatively, when a function of acircuit is specified, the circuit is disclosed as one embodiment of theinvention even when a connection portion is not specified, and oneembodiment of the invention can be constituted.

Note that in this specification and the like, part of a diagram or textdescribed in one embodiment can be taken out to constitute oneembodiment of the invention. Thus, in the case where a diagram or textrelated to a certain portion is described, the contents taken out frompart of the diagram or the text are also disclosed as one embodiment ofthe invention, and one embodiment of the invention can be constituted.The embodiment of the present invention is clear. Therefore, forexample, in a diagram or text in which one or more active elements(e.g., transistors or diodes), wirings, passive elements (e.g.,capacitors or resistors), conductive layers, insulating layers,semiconductor layers, organic materials, inorganic materials,components, devices, operating methods, manufacturing methods, or thelike are described, part of the diagram or the text is taken out, andone embodiment of the invention can be constituted. For example, from acircuit diagram in which N circuit elements (e.g., transistors orcapacitors; N is an integer) are provided, it is possible to take out Mcircuit elements (e.g., transistors or capacitors; M is an integer,where M<N) and constitute one embodiment of the invention. For anotherexample, it is possible to take out M layers (M is an integer, whereM<N) from a cross-sectional view in which N layers (N is an integer) areprovided and constitute one embodiment of the invention. For anotherexample, it is possible to take out M elements (M is an integer, whereM<from a flow chart in which N elements (N is an integer) are providedand constitute one embodiment of the invention. For another example, itis possible to take out some given elements from a sentence “A includesB, C, D, E, or F” and constitute one embodiment of the invention, forexample, “A includes B and E”, “A includes E and F”, “A includes C, E,and F”, or “A includes B, C, D, and E”.

Note that in the case where at least one specific example is describedin a diagram or text described in one embodiment in this specificationand the like, it will be readily appreciated by those skilled in the artthat a broader concept of the specific example can be derived.Therefore, in the diagram or the text described in one embodiment, inthe case where at least one specific example is described, a broaderconcept of the specific example is disclosed as one embodiment of theinvention, and one embodiment of the invention can be constituted. Theembodiment of the present invention is clear.

Note that in this specification and the like, what is illustrated in atleast a diagram (which may be part of the diagram) is disclosed as oneembodiment of the invention, and one embodiment of the invention can beconstituted. Therefore, when certain contents are described in adiagram, the contents are disclosed as one embodiment of the inventioneven when the contents are not described with text, and one embodimentof the invention can be constituted. In a similar manner, part of adiagram, which is taken out from the diagram, is disclosed as oneembodiment of the invention, and one embodiment of the invention can beconstituted. The embodiment of the present invention is clear.

Example 1

In this example, the thin storage battery (lithium-ion secondarybattery) described in Embodiment 1 was fabricated as a power storagedevice of one embodiment of the present invention. The initial chargeand discharge characteristics of the lithium-ion secondary battery andthe charge and discharge characteristics of the lithium-ion secondarybattery subjected to a bending test using a bend tester were evaluated.

The lithium-ion secondary battery was fabricated according to Embodiment1 using LiCoO₂ as a positive electrode active material, graphite as anegative electrode active material, and an embossed aluminum laminatefilm. The lithium-ion secondary battery obtained according to Embodiment1 includes six current collectors each having one surface provided witha positive electrode active material layer and six current collectorseach having one surface provided with a negative electrode activematerial layer. The thickness of the lithium-ion secondary battery isapproximately 2.1 mm. Table 1 shows the size and the like of thebattery.

TABLE 1 Voltage 3.7 V Capacity about 300 mAh External Thickness 2.1 mmdimension (except Height 75 mm lead portion) Width 60 mm Weight about11.5 g

FIG. 21A is a photograph of the appearance of the bend tester. FIG. 21Bshows the state where the fabricated lithium-ion secondary battery isplaced on the tester. The tester includes a cylindrical supporting bodywith a radius of curvature of 40 mm extending in the depth directionunder the lithium-ion secondary battery in a center portion. The testeralso includes an arm extending in the right direction and an armextending in the left direction. End portions of the arms aremechanically connected to holding plates. By moving the end portions ofthe arms up or down, the holding plates can be bent along the supportingbody. The bending test of the lithium-ion secondary battery wasperformed with the lithium-ion secondary battery sandwiched between thetwo holding plates. Thus, moving the end portions of the arms up or downallows the lithium-ion secondary battery to be bent along thecylindrical supporting body. Specifically, lowering the end portions ofthe arms permits the lithium-ion secondary battery to be bent with aradius of curvature of 40 mm. Since the lithium-ion secondary batterywas bent while being sandwiched between the two holding plates,unnecessary force except bending force was able to be prevented frombeing applied to the lithium-ion secondary battery. Furthermore, bendingforce was able to be uniformly applied to the whole lithium-ionsecondary battery.

The bending test was performed at intervals of 10 seconds in the rangeof radius of curvature from 40 mm to 150 mm. The charge and dischargecharacteristics were evaluated at 25° C. after the secondary battery wasdismounted from the tester. Charging was performed at a constant currentof 0.2 C (69 mA) until the voltage reached an upper voltage limit of 4.1V and then performed at a rate of 0.01 C (3 mA) until the secondarybattery was fully charged. Discharging was performed at a rate of 0.2 C(69 mA) until the voltage reached a lower voltage limit of 2.5 V.

Here, a charge rate and a discharge rate will be described. For example,in the case of charging a secondary battery with a capacity of X [Ah] ata constant current, a charge rate of 1 C means the current value I [A]with which charging is terminated in exactly 1 hour, and a charge rateof 0.2 C means I/5 [A] (i.e., the current value with which charging isterminated in exactly 5 hours). Similarly, a discharge rate of 1 C meansthe current value I [A] with which discharging is ended in exactly 1hour, and a discharge rate of 0.2 C means I/5 [A] (i.e., the currentvalue with which discharging is ended in exactly 5 hours).

Table 2 shows the results of the bending test. Note that dischargecapacities (mAh/g) shown in Table 2 are each a value per unit weight ofthe positive electrode active material.

TABLE 2 Number of times Discharge Discharge Capacity of bending capacitycapacity maintenance rate (times) (mAh) (mAh/g) (%) 0 336.5 133.3 1001000 335.6 132.9 99.7 3000 333.5 132.1 99.1 6000 331.1 131.1 98.35 10000329.3 130.4 97.82

X-ray CT photographs were taken after bending was performed 0 times,1000 times, 3000 times, 6000 times, and 10000 times and whether theinside was damaged was determined. FIGS. 22A to 22E show the respectiveX-ray CT photographs.

FIG. 22F is a photograph of the appearance of the lithium-ion secondarybattery after the bending test was performed 10000 times. FIG. 22G showsthe charge and discharge characteristics.

It was confirmed that the lithium-ion secondary battery using theembossed film as the exterior body did not have any damage to itsappearance or its internal structure even after being subjected to thebending test 10000 times and the charge and discharge curves reveal noabnormality.

Example 2

In this example, a thin storage battery (lithium-ion secondary battery)including a positive electrode active material different form that inExample 1 was fabricated. The initial charge and dischargecharacteristics of the lithium-ion secondary battery and the charge anddischarge characteristics of the lithium-ion secondary battery subjectedto a bending test using a bend tester were evaluated.

The lithium-ion secondary battery was fabricated according to Embodiment1 using LiFePO₄ as a positive electrode active material, graphite as anegative electrode active material, and an embossed aluminum laminatefilm. The lithium-ion secondary battery obtained according to Embodiment1 includes 10 current collectors each having one surface provided with apositive electrode active material layer and 10 current collectors eachhaving one surface provided with a negative electrode active materiallayer. The thickness of the lithium-ion secondary battery isapproximately 3 mm. Table 3 shows the size and the like of the battery.

TABLE 3 Voltage 3.2 V Capacity about 300 mAh External Thickness 3 mmdimension (except Height 75 mm lead portion) Width 60 mm Weight About 16g

The charge and discharge characteristics were evaluated at 25° C. afterthe secondary battery was dismounted from the tester. Charging wasperformed at a constant current of 0.2 C (78 mA) until the voltagereached an upper voltage limit of 4.0 V. Discharging was performed at arate of 0.2 C (78 mA) until the voltage reached a lower voltage limit of2.0 V.

Table 4 shows the results of the bending test. Note that dischargecapacities (mAh/g) shown in Table 4 are each a value per unit weight ofthe positive electrode active material.

TABLE 4 Number of times Discharge Discharge Capacity of bending capacitycapacity maintenance rate (times) (mAh) (mAh/g) (%) 0 315.9 138.7 1001000 314.4 138 99.5 3000 312.9 137.4 99.06 6000 311 136.5 98.41 10000309 135.7 97.84

X-ray CT photographs were taken after bending was performed 0 times,1000 times, 3000 times, 6000 times, and 10000 times and whether theinside was damaged was determined. FIG. 23A to 23E show the respectiveX-ray CT photographs.

FIG. 23F is a photograph of the appearance of the lithium-ion secondarybattery after the bending test was performed 10000 times. FIG. 23G showsthe charge and discharge characteristics.

It was confirmed that the lithium-ion secondary battery using theembossed film as the exterior body did not have any damage to itsappearance or its internal structure even after being subjected to thebending test 10000 times and the charge and discharge curves reveal noabnormality, as in Example 1.

Example 3

A lithium-ion secondary battery that includes LiCoO₂ as a positiveelectrode active material and has the same structure as the lithium-ionsecondary battery in Example 1 was subjected to a bending test 1000times while being charged at 0.2 C from the start of charging to thetermination of charging. FIG. 24A shows the charge characteristics ofthe lithium-ion secondary battery.

In addition, the lithium-ion secondary battery was subjected to thebending test 1000 times while being discharged (at 0.2 C) from the startof charging to the end of discharging (the end voltage: approximately2.5 V). FIG. 24B shows the discharge characteristics of the lithium-ionsecondary battery.

The results shown in FIGS. 24A and 24B reveal that there was no adverseeffect such as a voltage change even when the bending test was performedduring charging and discharging.

This application is based on Japanese Patent Application serial no.2013-219546 filed with the Japan Patent Office on Oct. 22, 2013,Japanese Patent Application serial no. 2014-095169 filed with the JapanPatent Office on May 2, 2014, Japanese Patent Application serial no.2014-107474 filed with the Japan Patent Office on May 23, 2014, andJapanese Patent Application serial no. 2014-133062 filed with the JapanPatent Office on Jun. 27, 2014, the entire contents of which are herebyincorporated by reference.

What is claimed is:
 1. An electronic device comprising: a housing; asecondary battery; and a display portion, wherein the display portioncomprises a region overlapping with the secondary battery and a regionnot overlapping with the secondary battery, wherein the secondarybattery overlaps with the housing, wherein the secondary batterycomprises an exterior body comprising a film, wherein the film comprisesa pattern including first depressions extending along a first directionand second depressions extending along a second direction intersectingthe first direction in both a first region and a second region, whereinthe first region is a center portion of the film, wherein the secondregion is an end portion of the film, wherein a depth of the firstdepressions in the first region is larger than a depth of the firstdepressions in the second region, and wherein a depth of the seconddepressions in the first region is larger than a depth of the seconddepressions in the second region.
 2. The electronic device according toclaim 1, wherein the secondary battery has flexibility, and wherein thedisplay portion has flexibility.
 3. The electronic device according toclaim 1, wherein the first direction and the second direction are notparallel to an edge in a width direction of the film.
 4. The electronicdevice according to claim 1, wherein the film is a single-layer film ora layered film comprising a metal film, a plastic film, a hybridmaterial film containing an organic material and an inorganic material,or a carbon-containing film.
 5. The electronic device according to claim1, wherein the film is an aluminum film.
 6. The electronic deviceaccording to claim 1, wherein a range of radius of curvature of thesecondary battery is from 40 mm to 150 mm.
 7. The electronic deviceaccording to claim 1, wherein the display portion comprises alight-emitting element.
 8. The electronic device according to claim 1,wherein the second region is in contact with an adhesive layer.
 9. Theelectronic device according to claim 1, wherein the secondary batterycomprises: a positive electrode current collector; a positive electrodeactive material layer; a negative electrode current collector; and anegative electrode active material layer.
 10. An electronic devicecomprising: a housing comprising a curved surface; a secondary batterycomprising a curved surface; and a display portion comprising a curvedsurface, wherein the display portion comprises a region overlapping withthe secondary battery and a region not overlapping with the secondarybattery, wherein the secondary battery overlaps with the housing,wherein the curved surface of the display portion is along the curvedsurface of the housing, wherein the curved surface of the secondarybattery is along the curved surface of the housing, wherein thesecondary battery comprises an exterior body comprising a film, whereinthe film comprises a pattern including first depressions extending alonga first direction and second depressions extending along a seconddirection intersecting the first direction in both a first region and asecond region, wherein the first region is a center portion of the film,wherein the second region is an end portion of the film, wherein a depthof the first depressions in the first region is larger than a depth ofthe first depressions in the second region, and wherein a depth of thesecond depressions in the first region is larger than a depth of thesecond depressions in the second region.
 11. The electronic deviceaccording to claim 10, wherein the first direction and the seconddirection are not parallel to an edge in a width direction of the film.12. The electronic device according to claim 10, wherein the film is asingle-layer film or a layered film comprising a metal film, a plasticfilm, a hybrid material film containing an organic material and aninorganic material, or a carbon-containing film.
 13. The electronicdevice according to claim 10, wherein the film is an aluminum film. 14.The electronic device according to claim 10, wherein a range of radiusof curvature of the secondary battery is from 40 mm to 150 mm.
 15. Theelectronic device according to claim 10, wherein the display portioncomprises a light-emitting element.
 16. The electronic device accordingto claim 10, wherein the second region is in contact with an adhesivelayer.
 17. The electronic device according to claim 10, wherein thesecondary battery comprises: a positive electrode current collector; apositive electrode active material layer; a negative electrode currentcollector; and a negative electrode active material layer.